Obnoxious Posted September 15, 2005 Share Posted September 15, 2005 [math]f(x) = e^x[/math] I keep getting the silly answer of just X, when I know it is [math]e^x[/math] Link to comment Share on other sites More sharing options...
mezarashi Posted September 15, 2005 Share Posted September 15, 2005 The question is what again? Given a function, you want to derive that function. Or do you mean differentiation using first principles? What have you tried so far. Show what you've done to get your answer. Link to comment Share on other sites More sharing options...
Obnoxious Posted September 15, 2005 Author Share Posted September 15, 2005 I was given [math]y = e^x[/math] So I did this! [math]\ln y = x \ln e[/math] [math]dx/dy = 1/y[/math] [math]dy/dx = y[/math] Am I making some illegal moves? Link to comment Share on other sites More sharing options...
timo Posted September 15, 2005 Share Posted September 15, 2005 What are you trying to do? Link to comment Share on other sites More sharing options...
Klaynos Posted September 15, 2005 Share Posted September 15, 2005 I think I understand what you are trying to do, show that f(x) = ex And f'(x) = ex Are both true? [math]\frac {\ln y} {\ln e} = x[/math] You need to do that stage before you can differentiate it wrt y Link to comment Share on other sites More sharing options...
DQW Posted September 15, 2005 Share Posted September 15, 2005 I was given[math]y = e^x[/math] So I did this! [math]\ln y = x \ln e[/math] [math]dx/dy = 1/y[/math] [math]dy/dx = y[/math] Am I making some illegal moves? If you are allowed to use the derivative of the logarithm (which is no more fundamental than that of the exponent), you have correctly found the answer, dy/dx = y = e^x If you have to prove this from "more fundamental" results, I suggeswt you use the series expansion for e^x and differentiate term by term. Link to comment Share on other sites More sharing options...
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